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Martian Oceans

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Wade Hampton III

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Martian Oceans

PostSun Sep 16, 2018 6:19 pm

For some time, scientists have known that Mars was once a much warmer and
wetter environment than it is today. However, between 4.2 and 3.7 billion
years ago, its atmosphere was slowly stripped away, which turned the surface
into the cold and desiccated place we know today. Even after multiple missions
have confirmed the presence of ancient lake beds and rivers, there are still
unanswered questions about how much water Mars once had. One of the most
important unanswered questions is whether or not large seas or an ocean ever
existed in the northern lowlands. According to a new study by an international
team of scientists, the Hypanis Valles ancient river system is actually the
remains of a river delta. The presence of this geological feature is an
indication that this river system once emptied into an ancient Martian sea
in Mars' northern hemisphere.
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For the sake of their study, titled "The Hypanis Valles delta: The last
highstand of a sea on early Mars?" which recently appeared in the journal
Earth and Planetary Science Letters, the international team consulted data
from the Mars Reconnaissance Orbiter (MRO) and the 2001 Mars Odyssey probe
to investigate the morphology, sedimentary architecture, and depositional
environment of the Hypanis Valles region. This delta is what separates the
southern highlands from the northern lowlands, where an ancient ocean is
once believed to have existed – a theory which has remained unproven. Based
on data from the MRO's High Resolution Imaging Science Experiment (HiRISE)
instrument and the 2001 Odyssey's THermal EMission Imaging System (THEMIS),
the team found compelling evidence that a large body of water once covered
the northern third of Mars.
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As Joel Davis – a postdoctoral researcher in the Planetary Surface Group
at the Natural History Museum and a co-author of the paper – explained in
a recent NHM press release: "A Martian ocean means that Mars probably had
a very Earth-like water cycle, with rivers, lakes, and now oceans, all of
which probably interacted as part of a planet-wide system. We think this
Earth-like hydrological cycle was active about 3.7 billion years ago, and
started to shut down sometime after that. Our study is not definitive proof
for an ocean, but these geological features are very hard to explain without
one." Determining whether or not Mars had standing bodies of water in the
past has been no easy challenge, mainly because Mars lacks the kinds of
apparent indications of lakes and oceans on its surface (like fine-grained
sand deposits or clear shorelines). As a result, scientists have had to look
for other means of identifying where water flowed and sand was deposited,
which is where sedimentary fans come into play. In this case, the fan
identified was a river delta, which form when a river slows down in the
presence of a slower-moving or still body of water. This causes any small
sediments that are being carried by the river to settle on the ground and
form geological features (e.g. small islands at the mouth of the river)
over time. In the past, river deltas have been found on Mars, but only
in craters where water flowed into a lake.
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Case in point, the Curiosity rover, which has been studying the Gale Crater
since it landed there in 2012, has discovered abundant evidence that the
crater was once a lake. This evidence included clay minerals at the base of
Mount Sharp, as well as sedimentary deposits and channels discovered in the
crater wall and Mount Sharp that could only be explained by water flowing
into the crater. Thanks to their study, scientists can now say with certainty
that the Hypanis sedimentary fan is evidence of a standing body of water
large enough to be an ocean. Their study also indicates how the ocean
retreated as the climate gradually become colder and dryer. Basically, as
ocean levels dropped by nearly 500 meters, the Hypanis delta began growing
outwards as a result. Finally, they determined that roughly 3.6 billion years
ago, the water system dried up and disappeared, which is consistent with when
Mars lost most of its ancient atmosphere. Since that time, no water has
been able to exist on the surface in any form other than ice – with the
exception of an underground lake that was recently discovered. As Dr. Peter
Fawdon, a post doctoral research associate from the Open University and the
lead author of the study, explained:

"The research has significantly contributed to our understanding of the
climate on early Mars, which we now know went from having a water cycle
similar to that of Earth to being a cold, desert-like landscape in a
relatively short period. We would like to gain a better understanding of
how many of these fluvial deltas exist on Mars so that we can determine
the position and size of its ancient seas." This study has not only provided
definitive evidence of their being an ocean on Mars, it is also significant
in that the shoreline of this ancient ocean is close to where the ExoMars
2020 and Mars 2020 rovers will be landing in the coming years. The fact
that an ocean once existed there increases the odds that these rovers will
find evidence of past Martian life – which is their primary goal. Over the
course of the last century, our collective understanding of Mars has changed
dramatically. Once thought to be a planet crisscrossed by canals and inhabited
by little green men, the first robotic missions to the Red Planet revealed a
frozen landscape that was hostile to life. However, in recent decades, evidence
has emerged that shows that Mars may have supported life in the past. And though
there may or may not be life there today, Mars remains a dynamic and fascinating
place that can teach us much about the history and evolution of our solar system.
However, if there are still microbes to be found on the Red Planet, the ExoMars
2020 and the Mars 2020 rovers are likely to be the ones that find it.

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White Man 1

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Re: Martian Oceans

PostSun Sep 16, 2018 8:38 pm

Congrats on your 1488th post, Wade!

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